John is the Berthold Beitz Professor in Human Rights and International Affairs at the Harvard Kennedy School of Government, and an Affiliated Professor in International Legal Studies at Harvard Law School.

In 2005, then United Nations Secretary-General Kofi Annan appointed John as his Special Representative for Business and Human Rights, a post he continued to hold under the UN administration of Ban Ki-Moon until the end of his term in June 2011. At the close of his mandate, John presented to the UN Human Rights Council a set of Guiding Principles for Business and Human Rights. The Council unanimously endorsed the Guiding Principles, establishing them as the authoritative global reference point on this issue.

John served from 1997 to 2001 as UN Assistant Secretary-General for Strategic Planning to Kofi Annan. Trained as a political scientist, he has made significant intellectual contributions to the study of international relations, focusing on the impact of economic and other forms of globalization on global rule making.